Java Web Applications

1. Java Web Applications

2. WAR • Web Archive • Introduced with servlet 2.2 specification • Portable deployment mechanism for web applications • Defines directory structure • Jar’d into a .war file for deployment • Uses XML deployment descriptor

3. Directory Structure find ./webbasics -print ./webbasics ./webbasics/WEB-INF ./webbasics/WEB-INF/classes ./webbasics/WEB-INF/classes/ejava ./webbasics/WEB-INF/classes/ejava/servlets ./webbasics/WEB-INF/classes/ejava/servlets/webbasics ./webbasics/WEB-INF/classes/ejava/servlets/webbasics/BonusServlet.class ./webbasics/WEB-INF/classes/ejava/servlets/webbasics/PurchaseServlet.class ./webbasics/WEB-INF/web.xml ./webbasics/WEB-INF/weblogic.xml ./webbasics/FormExample.html ./webbasics/MenuExample.html

4. Directory Structure (Cont) • WEB-INF • Contains web.xml deployment descriptor • Contains class files for web app (classes) • Contains .jar files for web app (lib) • Contains Tag Library Descriptors (tlds) • Cannot be served to client • Other directories store web content i.e. jsp/html files, images, sound, etc.

5. Deployment Descriptor (web.xml) <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 1.2//EN" "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd"> <web-app> <display-name>HTML Basics</display-name> <context-param> <param-name>weblogic.httpd.servlet.reloadCheckSecs</param-name> <param-value>1</param-value> </context-param> <servlet> <servlet-name>PurchaseServlet</servlet-name> <servlet-class>ejava.servlets.webbasics.PurchaseServlet</servlet-class> <init-param> <param-name>param1</param-name> <param-value>value1</param-value> </init-param> </servlet> <servlet> <servlet-name>BonusServlet</servlet-name> <servlet-class>ejava.servlets.webbasics.BonusServlet</servlet-class> </servlet> ...

6. Mapping Servlets to URLs (web.xml) … <servlet-mapping> <servlet-name>PurchaseServlet</servlet-name> <url-pattern>PurchaseAlias</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>BonusServlet</servlet-name> <url-pattern>BonusAlias</url-pattern> </servlet-mapping> ...

7. Declaring Default Pages (web.xml) … <welcome-file-list> <welcome-file>/welcome.html</welcome-file> </welcome-file-list> ...

8. Creating the .war file %cd c:\\weblogic/myserver/public_html/webbasics; \ %//c/jdk1.3/bin/jar cvf /webbasics.war * added manifest adding: FormExample.html(in = 467) (out= 257)(deflated 44%) adding: MenuExample.html(in = 486) (out= 274)(deflated 43%) adding: WEB-INF/(in = 0) (out= 0)(stored 0%) adding: WEB-INF/classes/(in = 0) (out= 0)(stored 0%) adding: WEB-INF/classes/ejava/(in = 0) (out= 0)(stored 0%) adding: WEB-INF/classes/ejava/servlets/(in = 0) (out= 0)(stored 0%) adding: WEB-INF/classes/ejava/servlets/webbasics/(in = 0) (out= 0)(stored 0%) adding: WEB-INF/classes/ejava/servlets/webbasics/BonusServlet.class(in = 2403) ( out= 1260)(deflated 47%) adding: WEB-INF/classes/ejava/servlets/webbasics/PurchaseServlet.class(in = 2585 ) (out= 1449)(deflated 43%) adding: WEB-INF/web.xml(in = 1843) (out= 587)(deflated 68%) adding: WEB-INF/weblogic.xml(in = 412) (out= 227)(deflated 44%) adding: WEB-INF/web.xml~(in = 1071) (out= 366)(deflated 65%) adding: welcome.html(in = 183) (out= 103)(deflated 43%)

9. Summary • The web application format should be used for all web deployments • Standardized mechanism for web tier deployments

10. Java Servlets

11. Servlet Definition • “Web component, managed by a container, that generates dynamic content” • Request-Response mechanism modeled after HTTP • Required by J2EE v1.2 specification • Web Server configured to invoke servlets when specified URLs are accessed (servlet mapping) • HTML Forms • Java programs

12. Architecture Get/Post Request Request Web Browser Web Server Servlet Container HTML Page Reply Servlet

13. Servlet Benefits • Efficiency • run as threads vs. CGI processes • Written in Java • can use any Java API such as JDBC, EJB, RMI, etc. • Portability • supported by many web/application servers • Simplicity • Provides support for common operations including session management

14. Servlet Container • Provides the execution environment for a servlet • Must support HTTP as the request/response protocol • HTTP 1.1 support strongly recommended by spec • May support HTTPS (HTTP over SSL) • Can be installed directly in a web server or as an add-on using web server extension mechanisms • May impose security constraints on servlet

15. My First Servlet import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloWorld extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out = response.getWriter(); out.println(“Hello World”); } }

16. Notes • Default return mime type is text/plain • Can also implement doPost • Same arguments • What if you want to answer to both? • Running the servlet • Compile • You will need the java 2 enterprise edition jar in your classpath • Put class into WEB-INF/classes • Put in servlet mapping and class info in WEB-INF/web.xml • Invoke  http://host/context/servletmapping

17. Key Servlet Classes

18. Another Example import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloWorld extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType(“text/html”); PrintWriter out = response.getWriter(); out.println(“<HTML>\n” + “<HEAD><title>Hello WWW</title></HEAD>\n” + “<body>\n” + “<h1>Hello World!</h1>\n” + “</body></html>”); } }

19. Requests and Responses

20. The HttpServletRequest Object • Form parameters • String choice=request.getParameter(“Product”); • String getParameter(String key) • String[] getParameterValues(String key) • Enumeration getParameterNames() • Cookies • Cookie[] = request.getCookies() • getName(), getValue() • Binary Data • InputStream is = request.getInputStream() • Character Data • Reader r = request.getReader()

21. The HttpServletResponse Object • void setContentType(String type) • void setContentLength(int len) • PrintWriter getWriter() • ServletOutputStream getOutputStream() • Used to send binary data back to client • void setHeader(String name, String value) • Other methods as well

22. Servlet Implementation package ejava.servlets.webbasics; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class PurchaseServlet extends HttpServlet { public void init(ServletConfig config) throws ServletException { super.init(config); log("BonusServlet:init(config)"); }

23. Servlet (Cont) public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, java.io.IOException { response.setContentType("text/html"); java.io.PrintWriter out = response.getWriter(); out.println("<html><head><title>"); out.println("Purchase Servlet"); out.println("</title></head><body>"); if (request.getParameter("BUYCMD") != null) { String product = request.getParameter("Product"); out.println("<p><b>purchased product:</b>"+product); } out.println("</body></html>"); out.close(); }

24. Performance Issues • Strings are immutable • New string object is created for each string • Also for each concatenation of 2 strings •  a lot of object creation and cleanup • Use a single StringBuffer object • Use append() method to add text to it • Use flush method to push output to client

25. Organizational Issues • WEB-INF/classes can get crowded • Use java packages to clean things up • package mypackage; //place at top of file • Put classes in WEB-INF/classes/mypackage • Set up servlet mapping in WEB-INF/web.xml • Invoke http://host/context/servletmapping

26. Headers and CGI variables • Request object has methods to access • String value getHeader(String name) • Others • PrintEnv code • http://localhost:8080/ServletsAndJSP/TestGetPostServlet.html

27. Cookies • Use the Cookie class • Constructor • Cookie(String name, String value) • Cookie Methods • String getDomain() or void setDomain(String dom) • String getName() or void setName(String name) • String getValue() or void setValue(String value) • String getPath() or void setPath(String path) • boolean getSecure() or void setSecure(boolean flag) • int getMaxAge() or void setMaxAge(int seconds)

28. Cookies • Create a cookie • Construct it • Set values • Add the cookie to the response before content type • response.addCookie(Cookie theCookie) • Get Cookies from request • Cookie[] cookies = request.getCookies()

29. Sessions • High level API • HttpSession object • Built on top of cookies or URL-rewriting • You don’t have to worry which one • Convenient place to store information • Arbitrary objects • Associated with each session

30. The Session API • Get the HttpSession object • HttpSession session = request.getSession(true); • true automatically creates one if one doesn’t exist • Get and Set information using HttpSession methods • Object getAttribute(String name) • void setAttribute(String name, Object value) • void removeAttribute(String name) • String[] getAttributeNames() • String getID() • boolean getId() • long getCreationTime() and long getLastAccessedTime() • int getMaxInactiveInterval() and void setMaxInactiveInterval(int sec) • void invalidate()

31. Example: Toy Shop • http://localhost:8080/ServletsAndJSP/ToyShop.html

32. The Servlet Life Cycle • Initialization • void init() or • void init(ServletConfig config) • Be sure to call super.init(config) on first line • doXxx methods are called (doGet, doPut, etc.) • Consider if you need single thread • public class YourServlet extends HttpServlet implements SingleThreadModel • Destruction • void destroy() • don’t rely on this. The server could crash

33. Servlet Context • Servlet may wish to interact with the host server • GenericServlet::getServletContext() • getMimeType( String file ) • getServlet(String name) : Servlet • log(Exception, String) • log(String)

35. Redirection • Web Browser redirection • resp.sendRedirect(String url) • resp.sendError(int code, String message) • Server-Side • RequestDispatcher rd = getServletContext().getRequestDispatcher(urlString); • rd.forward();

36. Request Dispatcher

37. Resources • Main Servlets Page • http://java.sun.com/products/servlet/ • Java Servlet Specification v2.2 • http://java.sun.com/products/servlet/2.2/index.html • Marty Hall’s servlet tutorial • http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/